H. K. Hall Jr. and M. A. Howey, Polym. Bull., vol. 12, pg. 427-431 (1984) report that aryl diazonium salts polymerize p-methoxystyrene in nitrobenzene. No mention is made of cyanates or hyponitrites, or the ability to restart the polymerization.
H. Warson in two papers (Die Makromol. Chem., vol. 105, pg. 228-250 (1967)) reports that aryl diazonium compounds with either bisulfite or hypophosphorous acid will polymerize acrylonitrile.
P. R. Singh, et al., Tet. Lett., vol. 23, pg. 5191-5194 (1982) report the aryl diazonium ions react with nitrite ions to give free radical type intermediates. No mention is made of polymerization.
C. Walling, Free Radical in Solution, John Wiley & Sons, Inc., New York, 1957, pp. 518-519 and W. E. Bachmann and R. A. Hoffman, in R. Adams, Ed., Organic Reactions, Vol. II, John Wiley & Sons, Inc., New York, 1944, pp. 226-230 speculate that aryldiazohydroxides, which are said to be in equilibrium with their sodium salts when in contact with sodium hydroxide, decompose readily at room temperature to give free radicals.
In all of the above references, there is no mention of the use of diazotate, cyanate, hyponitrite "coagents", the use of these compounds for acrylic polymerizations, or the possibility of an "interruptible" polymerization.
U.S. Pat. No. 4,581,429, describes the use of a compound of the formula (here modified) R.sup.a.sub.2 N--O--X, wherein R.sup.a is a hindered alkyl group and X is a group containing at least one carbon atom. Although this compound can initiate acrylic polymerization, and the polymerization is interruptible, no mention is made of diazonium salts, diazotates, cyanates or hyponitrites.
U.S. Pat. No. 4,761,360 describes a light sensitive material containing a silver halide, a reducing agent, a polymerizable compound (vinyl monomer) and a silver diazotate. This mixture is reported to be stable (indeed it is said to be an advantage) until the material is exposed to light, and then heated, at which time the vinyl monomer is polymerized. In the instant process a silver halide is not present.
It is the object of this invention to provide a method for the polymerization of acrylic and maleimide monomers, by contacting the monomers with an aryl diazotate, a cyanate, or a hyponitrite, and an aryl diazonium salt or an N-halosuccinimide. This process, which may be carried out in a variety of ways, such as neat, in solution, or as an emulsion, may be restarted after the polymerization has stopped. This surprising property may be utilized to prepare block copolymers.